This invention relates to model airplanes and other flying toys, which are launched with the help of a tow line, specifically to a tow release system that automatically disengages the tow line upon detecting that the aircraft has reached a predetermined climbing position and height.
Many flying toys, and model airplanes are launched with the help of a tow line that is connected to the airplane through a hook. The tow line can be an extended elastic band, which propels the airplane to fly upon contraction. Alternatively, a non-elastic tow line can be driven by a winch. In either case, the tow line is released when the airplane reaches a certain climbing position. The quality of the free flight that follows is strongly influenced by the timing of the release and the climbing angle of the fuselage at the moment of the release.
Radio-controlled gliders are frequently launched by a tow line that is a combination of a long elastic band and an even longer tow string. One end of the tow line is attached to a ground-stake, while the other end terminates in a small tow ring. For take-off, the tow ring is attached to a hook on the bottom of the glider""s fuselage. This towing system, commonly known as xe2x80x9cHigh Startxe2x80x9d, can tow a glider to several hundred feet in height before releasing it for a free flight. During the tow, the pilot must continuously adjust the elevator position on the glider in order to avoid an excessive climb angle that would result in a wing stall or a premature release of the tow line. When the pilot decides to release, he or she first has to set the elevator position so that it forces the glider into a dive for a few seconds. This reduces the tension in the tow line. Then, he or she has to tilt the glider""s nose up, in order to make the tow ring slide off the hook.
Other radio-controlled gliders found in the prior art utilize a tow line which is propelled by a closed-loop string which, in turn, is pulled by a winch. This tow system requires an electric motor, a speed controller, and a large electric battery. It has the advantage of being able to tow the glider at a steady speed, but the pilot still has the responsibility to continuously adjust the climb angle in order to avoid a premature release or a wing stall. To release the tow ring from the tow hook, the pilot has to execute the same sequence of radio-controlled flight maneuvers, as described above.
For highly experienced radio-control pilots, performing these sensitive maneuvers is part of the fun. For less adept pilots or students, however, a misguided take-off can cost a sometimes very expensive model airplane. A release system, that automatically detects the appropriate release time and disengages the tow line in a reliable fashion, could be of great value for such users, since it would let them concentrate on piloting the glider in free flight, while they are acquiring the necessary skills for complete control.
An even more important use of an automatic tow release system would be for the launching of model gliders, toy airplanes, and other flying toys that do not have radio control. Such models can provide inexpensive and educational entertainment for everyone, regardless of economical status or flying experience.
To the best of our knowledge, there has been no automatic tow release system presented in prior art that releases the tow line at any user-determined climbing position and does so in a reproducible and reliable manner.
Small gliders are frequently launched with a hand-held rubber band, hooked to a simple notch on the lower part of the fuselage, as seen in U.S. Pat. Nos. 4,863,412 and 5,383,805. This type of hook mechanism releases the rubber band as soon as the speed of the glider exceeds that of the contraction of the rubber band. This type of launching is similar to shooting an arrow, whereby the trajectory of the free flying airplane is determined by the aiming of the user. Because of the limited length of the user""s arms, this type of launching system utilizes only a short rubber band and no tow string. Therefore, it can propel the flying toy to a relatively low height, and speed, compared to more complex towing systems.
Another method to launch a toy car or a toy airplane is given in U.S. Pat. No. 5,433,641. It uses the force of two strings being pulled apart by a sudden lateral movement of the user""s hands and since the toy is riding both strings and a rigid rail, it is propelled forward along the rail. This launching method can propel a car toy for only a few feet on the floor or make a toy airplane reach only a few feet in height thus having the same limitations mentioned in the previous paragraph. To launch a model glider you may need to attain several hundred feet in height before the gliding free flight can begin. Another disadvantage of this launch method is that it does not have a tow release mechanism that controls the flight attitude of the toy airplane while it is climbing; the attitude of the toy airplane is controlled only while it is riding the short rigid rail.
Another use of strings to launch a toy airplane or a toy missile is given in U.S. Pat. No. 2,638,708. It uses a hand-held handle that has a rotating disc with two strings attached to it and with the other ends of the two strings attached to a small rotating element inside the toy to be launched. By whirling the toy, a centrifugal force is imparted to it until a large velocity is achieved, similar to the traditional sling and stone launcher. To release the missile from the strings, the position of a trigger lever is changed in the hand held handle which stops the disc from rotating and this in turn changes the relative angular position of the two strings. At the other end of the two strings this creates a corresponding rotational movement in the small rotating element inside the missile causing the small rotating element to become detached from the toy airplane leading to its release from the two strings.
A disadvantage of this launching method and its release mechanism is that in order to whirl around the flying toy, it must use short strings of a few feet in length; thus the flying toy is released at a height of only a few feet; it is not possible to whirl around a model glider with long strings and make it reach a height of several hundred feet before the release mechanism detaches the strings so that it starts its free gliding flight. Another disadvantage is that this string release mechanism uses two strings, so if they were several hundred feet long, they would entangle easily causing a differential elongation that causes errors in the angular position of the release mechanism leading to an inaccurate release.
An advantage of the presently proposed release mechanism over this centrifugal launching method and string release mechanism, is that it can be used in connection with a single string tow line to tow the model glider to several hundred feet in height. This avoids the use of the heavier two string system and avoids the problem of having two very long lines becoming entangled and differentially elongated causing errors in the angular positions of the release mechanism causing an inaccurate release.
It is for this reason, that the xe2x80x9cState of the Artxe2x80x9d launching method for model gliders, known commercially as xe2x80x9cHi-startxe2x80x9d is preferred. It is a tow system made up with a single long elastic element, such as a rubber-band or latex tube, tied to an even longer single tow line, such as a nylon fishing line, with a total length of 200 to 300 feet. The end of the rubber-band is attached to a ground stake and the end of the tow line is attached to small steel ring. To launch a model glider, the steel ring is inserted into a single hook located on the body of the model glider; then the user walks several feet stretching the latex tube to its elastic limit. When the user lets the glider be pulled by the elastic element-tow line system it will rise gradually to several hundred feet in height. As mentioned before, the disadvantage of the single hook tow release system used in the xe2x80x9cHigh-startxe2x80x9d method is that it can not control automatically the fuselage angle during the climbing phase; this can easily cause a wing stall or a premature release before the maximum height is reached. It is the objective of the present automatic tow release system to overcome this difficulties.
The use of a long tow line is desirable for launching model airplanes, even if they are not equipped with radio control, because of the great height it provides. In such cases, however, the use of a simple ring-and-hook connection results in a tow system that does not release consistently at the desired height, speed, and flight path angle. The fuselage""s climb angle during take-off depends strongly on the relative air speed over the glider. This, in turn, depends on the wind speed, wind direction, and the amount of stretch given to the elastic band, or the speed of the winch. Furthermore, a tow system, comprising a simple tow hook and a tow ring, does not sense the fuselage""s climb angle with respect to the ground, therefore such a tow system can not be pre-set to release the tow line when the glider is in the optimum position and speed to initiate the longest possible glide. These release conditions occur when the glider is at the maximum possible height, with its speed near its gliding speed, and with the fuselage in an almost horizontal position. What typically happens when one attempts to launch a non-radio-controlled airplane in this fashion is that the plane releases prematurely at a relatively low height, and high speed, with its fuselage in an almost vertical position. As a result, it either makes a loop upon release and thereafter it quickly lands, or it dives and crashes.
Consequently, for model planes with no radio control, it is very important to have an automatic tow release system. The user of such system could predetermine the height, at which he or she wishes the airplane to disengage from the tow line. For the longest possible free flight, the glider would release at maximum height. For a loop, it would release at a sufficient height to avoid a crash and while it is still in the accelerating climbing position.
Accordingly, it is an object of the present invention to provide an automatic tow release system for model aircraft launched by a tow line which comprises novel means for (a) automatically sensing the climb angle of the fuselage, and the angle of the tow line relative to the ground, (b) continuously and automatically adjusting the climb angle of the fuselage to the appropriate level based on the tow line angle, in order to avoid a premature release or a wing stall, and (c) automatically releasing the tow line when the aircraft reaches a predetermined climbing position.
Another object of the present invention is to provide a low-cost, reliable automatic tow release system for model aircraft which does not rely on radio control or time delay mechanisms, and comprises no complicated moving parts.
Still another object of the present invention is to provide an automatic tow release system which can be set to release the aircraft in optimum position for a slow gliding flight or for a quick loop, depending on the user""s intention.
In keeping with these objects, and with others which will become apparent hereinafter, some features of the preferred embodiment of the present invention reside, briefly stated, in an automatic tow release system, comprising a primary and a secondary control string, both are connected to the tow line at one end and to a connecting body at the other end; a primary and a secondary hook, both are attached to the connecting body; and a primary and a secondary hook receptacle, both are installed on the bottom of the fuselage. The primary and secondary hooks are connected to the primary and secondary hook receptacles, respectively, during towing.
Other important features of the preferred embodiment are that the primary and secondary hooks are installed near the rear and front ends of the connecting body, respectively; and the primary control string is connected to the connecting body below the primary hook, while the secondary control string is connected to the connecting body below the secondary hook. Consequently, when the pulling force of the tow line is conveyed mostly through the primary control string, it acts mainly on the primary hook. When the pulling force is conveyed mostly through the secondary control string, it acts mainly on the secondary hook.
Another feature of the present invention is that the geometry between the fuselage, the connecting body and the control strings is designed so, that the pulling force of the tow line is conveyed to the aircraft initially by the primary control string, and it is transferred gradually to the secondary control string as the glider is climbing.
Still another important feature of the present invention is that the design of the primary and secondary hooks comprises a means for triggering the release of the tow line when the pulling force is acting mostly on the secondary hook. In the preferred embodiment, this means is achieved by making the two hooks have different angles relative to the connecting body. Namely, the primary hook has an angle that is significantly smaller than the angle of the secondary hook. While the pulling force of the tow line is acting mostly on the primary hook, it cannot slide out of the primary hook receptacle because of its small angle. When the pulling force acts mainly on the secondary hook, the hook assembly is released.
Other features of the tow release system include that, because of its geometric design, it controls the climb angle of the fuselage throughout the tow, keeping the aircraft safe.
The novel features which are considered characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, will be best understood from the following description of the preferred embodiment when read in connection with the accompanying drawings.